Wardian Heaters

Barry Meyers-Rice (barry@as.arizona.edu)
Tue, 1 Feb 94 08:25:59 MST

>> project, I'd buy a thermostat (a $30 Dayton one would be fine), hook it up
>> to a light bulb, and be done with it. Maybe I'd rig a small light-tight

>That's a great suggestion. Do you feel the humidity could cause any sort
>of fire hazard? Are there fixtures designed for this sort of thing?

Well, you'd want to be careful when you rig this up since you *are* messing
with water and electricity. Humidity is not a problem, unless you actually have
droplets of water forming on the bulb. Hmmm...the more I think about this, the
more likely I see the hazard of getting droplets of water shorting the bulb.
So here is plan #2. Go to an electronics shop, something bigger than Radio
Shack if you can, and look for nice sturdy resistors rated for 110V.
Choose a resistance like a couple of hundred ohms, since P=IV, V=IR, so
P=V*V/R, so 100 ohms will give you about a 100W heater. There's probably a
couple of factors of sqrt(2) in those equations, but it won't really matter.

Then connect wires to each end of the resistor, preferably by soldering. And
then (and here's the important step) coat any exposed wires with some kind
of nonconductor. First I thought of wax, but maybe that would melt. Maybe mix
up some epoxy. But anyway, coat the exposed metal surfaces.

Finally, while you're at the electronic shop, buy a fuse and a little fuse
holder. BUS fuses would be fine. The fuse holder will be cheap, just a few
bucks, same for a box of fuses. Buy fuses rated for maybe 2 Amps. In any
event, make sure the rating is about 1.5 or 2 times the current draw, which
will be about I=V/R, where R is your resistance and V is about 110 V.

The reason I said it's not too important what the resistance (and therefore
power) of your heater is, is that you'll have a thermostat regulating things.

Now that I mentioned Dayton Brand, does anybody have a 1-800 number for them?
They make, IMHO, the best thermostats around for greenhouse use.

>but on the big scale of things...the way big scale of things,
>matter and EM radiation (2.9 K stuff) are pretty much completely
>decoupled, and the heat capacity of the universe is completely
>dominated by the latter. I think everyone should keep this
>in mind when designing their carnivorous plant enclosures!

Well Dave, don't get your cosmic eras confused. Decoupling is not the same
thing as matter dominated/energy dominated. We live in a presently matter-
dominated universe. Anyway, I think a more important consideration, especially
in designing Wardian boxes, is the effect of WIMPS. After all, if you don't
keep the Universe closed, the humidity is going to drop, right? :)